fix type of extended argument array to pselect6 syscall

this only matters on x32 (and perhaps future 32-on-64 abis for other
archs); otherwise the type is long anyway. the cast through uintptr_t
prevents nonsensical "sign extension" of pointers, and follows the
principle that uintptr_t is the canonical integer type to which
pointer conversion is safe.

src/select/pselect.c

 #include <sys/select.h>
 #include <signal.h>
+#include <stdint.h>
 #include "syscall.h"
 #include "libc.h"
 
 int pselect(int n, fd_set *restrict rfds, fd_set *restrict wfds, fd_set *restrict efds, const struct timespec *restrict ts, const sigset_t *restrict mask)
 {
-	long data[2] = { (long)mask, _NSIG/8 };
+	syscall_arg_t data[2] = { (uintptr_t)mask, _NSIG/8 };
 	struct timespec ts_tmp;
 	if (ts) ts_tmp = *ts;
 	return syscall_cp(SYS_pselect6, n, rfds, wfds, efds, ts ? &ts_tmp : 0, data);